Abstract Java Kafka client metrics via Producer/ConsumerMetrics

[dfakhritdinov]

The PR addresses issue evolution-gaming/smetrics#237 and based on @Z1kkurat PR #324, thanks for inspiration!

Goal of the change is in exposing Java Kafka client metrics in the same way as native skafka metrics.

Native metrics represented by ProducerMetrics and ConsumerMetrics traits, their implementation require com.evolutiongaming.smetrics.CollectorRegistry. This approach allows decoupling metrics and their collector implementation, which is Prometheus (at least smetrics provides Prometheus support, other implementations also possible).

Java Kafka client metrics can be exposed to Prometheus with help of com.evolutiongaming.skafka.metrics.KafkaMetricsCollector - Prometheus collector was placed in separate module with dependency on Prometheus client. This PR aimed integrate the collector with ProducerMetrics and ConsumerMetrics traits in main skafka module (one without dependency on Prometheus client). For that new methods were introduced in both traits with default empty implementation. Actual implementation is in helper objects ProducerMetricsOf and ConsumerMetricsOf respectively.

Example:

import ConsumerMetricsOf.*

val config: ConsumerConfig = ???
val registry: CollectorRegistry = ???   // Prometheus client
val metrics: ConsumerMetrics[IO] = ???

for {
  metrics   <- metrics.exposeJavaClientMetrics(registry)
  consumerOf = ConsumerOf.apply1(metrics1.some) 
  consumer  <- consumerOf(config)
} yield ???

[coveralls]

Pull Request Test Coverage Report for Build 9937634721

Details

• 19 of 26 (73.08%) changed or added relevant lines in 5 files are covered.
• 4 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.2%) to 96.88%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
modules/metrics/src/main/scala/com/evolutiongaming/skafka/metrics/KafkaMetricsRegistry.scala	0	7	0.0%

Files with Coverage Reduction	New Missed Lines	%
skafka/src/main/scala/com/evolutiongaming/skafka/consumer/ConsumerLogging.scala	2	92.12%
skafka/src/main/scala/com/evolutiongaming/skafka/producer/ProducerMetrics.scala	2	98.21%

Totals
Change from base Build 9220432565:	-0.2%
Covered Lines:	2205
Relevant Lines:	2276

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💛 - Coveralls